Unlike the method referred to as anchor tufting which includes arranging the tufts in a U-shaped configuration and, with the aid of small metal anchor plates placed between the legs of the U-shaped tufts, inserting them into a blind-end bore in the bristle carrier where they are fastened by shooting the anchor plate into opposite side walls of the blind-end bore, the bristles are not arranged in U shape in the anchor-free tufting method. In the method referred to as anchor-free tufting the bristles are seated with their one ends in the holes in the bristle carrier while the opposite ends project out freely, forming the working ends of the bristles. The ends seated in the holes are fastened, for example, by welding or adhesive bonding to the bristle carrier.
From DE 195 45 030A1 there is known a brush with inserted tufts fastened by means of anchor plates. Perforating dies, with which it is possible to form holes of a cross section exceeding that of a single tuft, are provided to form at least a part of the tuft holes in the bristle carrier. Toward their one end these perforating dies have indentations that are open at the edge to create an intermediate bar or a partition wall within the complete hole cross section. Hence the complete hole is formed of hole sub-sections with a cross section corresponding in each case to approximately the cross section of the tuft. It is thus possible to manufacture brushes with bristle sub-fields made up of several individual tufts. The intermediate bars or partition walls are comprised of the same material as the bristle carrier itself, which is generally plastic. To fasten the tufts with the anchor plates it is however necessary for these plastic partition walls to be of sufficient thickness so as not to bend during the tufting operation. Consequently, a relatively wide gap remains between the individual tufts inserted in the hole subsections with the result that, on the one hand, the tufts located in the complete hole cross section do not form a homogeneous field of bristles and, on the other hand, the stability of the individual bristles is reduced because they are no longer able to lend each other mutual support on account of the presence of the relatively thick plastic partition walls and the attendant gap formation.
A toothbrush with tufts fastened by the anchor-free tufting method is presented in WO 99/55194 or EP 0972464A1, for example. Such brush heads with anchor-free fastened tufts are capable of improvement in several respects:
One problem concerns the service life of such brushes. Premature wear occurs as the result of a relatively severe movement of the bristles, particularly in the case of tufts with a non-circular outer contour. On account of the special fastening of the bristles the free and hence bendable length of the bristles at the one end of the bristles is bigger compared to tufts fastened by the anchor tufting method, with the result that otherwise identical bristles are easier to bend when secured by the anchor-free tufting method.
Movability also has an adverse effect on dental cleaning efficiency and reduces the subjectively perceived stiffness of the brush head. As a rule, higher cleaning forces are applied on account of the perceived softness of the brush head. Where electric toothbrushes are concerned, this can reduce the angle of oscillation of the brush head on account of play in the toothbrush gearing, thus impairing cleaning performance.
Room for improvement also exists with regard to appearance. With the anchor-free tufting method there is a risk of the bristles within a tuft being pushed over each other, making it impossible to perceive a clear-cut, colored border between color-segregated areas of tufts.